The present invention relates to an arrangement for sewage clarification by the activated sludge process, in particular with denitrification.
Sewage purification by the activated sludge process is normally carried out in large aeration tanks which are charged via delivery conduits having control weirs. Where appropriate, the large aeration tanks are charged from a preliminary clarification tank via inverted siphons to equalize the sewage flow.
A particularly useful type of sewage purification by the activated sludge process which provides successful denitrification and avoids formation of sludges which are difficult to settle is described in U.S. Pat. No. 4,793,930 and U.S. patent application Ser. No. 07/174,386, now issued as U.S. Pat. No. 5,019,266. According to this process, sewage is added at regular time intervals and in pulses of limited duration to the aeration tank, and for simultaneous denitrification the aeration is switched off or cut back until anoxic conditions are present. During this anoxic phase, nitrate present in the tank is substantially consumed, and sufficient reduction in the concentration thereof triggers resumption of aeration in the tank.